Is there just one correct way to calculate wing lift?

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    Lift Wings
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Discussion Overview

The discussion centers around the mechanisms of lift generation in wings, exploring whether there is a singular correct method to calculate lift. Participants examine various wing shapes, including curved and flat designs, and their implications for different flight conditions, including inverted flight. The conversation includes theoretical explanations, practical applications, and the role of aerodynamic principles.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants assert that wings generate lift due to the curvature of their shape, which causes air to flow faster over the top, while others challenge this by stating that flat wings can also produce lift under certain conditions.
  • There is a claim that if curved wings produce lift, then flying upside down should not be possible, which is contested by others who argue that both wing shape and angle of attack contribute to lift generation.
  • Some participants highlight that the Wright brothers' wings were not flat and that their design innovations included optimizing wing curvature.
  • It is noted that certain aircraft, particularly those designed for aerobatics, utilize symmetrical wing profiles that can generate lift in inverted flight.
  • One participant discusses the role of Newton's laws in explaining lift, emphasizing the necessity of downward air deflection and the impact of angle of attack.
  • Another participant critiques the application of the Coanda effect in the context of lift generation, arguing that it is misapplied and that viscosity plays a significant role in airflow adherence to wing surfaces.
  • There is a discussion regarding the efficiency of airfoils compared to flat wings, with some participants suggesting that a flat wing at a sufficient angle of attack could generate lift, but not as efficiently as a cambered wing.

Areas of Agreement / Disagreement

Participants express multiple competing views regarding the mechanisms of lift generation, with no consensus reached on a singular correct method or model. The discussion remains unresolved, with ongoing debate about the roles of wing shape, angle of attack, and aerodynamic principles.

Contextual Notes

Participants mention various assumptions regarding wing design and performance, including the dependence on specific flight conditions and the definitions of "better" in the context of different aircraft types. There are also references to unresolved mathematical steps and the complexity of aerodynamic interactions.

  • #61
DaveC426913 said:
No no. He is claiming the down wash of air is the only component needed to explain lift. He ignores the Bernoulli Principle.
If the Bernoulli Principle did not contribute to lift, then there would be no reason for a cambered wing, you would simply use a plank.

The Bernoulli principle describes pressures. Pressure x Area = Force, which is the lift force.

If you consider the down wash of air then what you are mainly interested in is how much air is pushed down and how fast it is pushed down, aka, it's momentum. Except, that you are dealing with a continuous process, so it's really momentum imparted to the air per unit of time. mv/t. since v/t is acceleration mv/t=ma

So, Bernoulli gives you force, Newton gives you mass x acceleration...Drum roll please...

F=ma
 
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  • #62
I don't want to take away from the fact that you are correct here, but I feel the need to point out that just because something is dimensionally correct doesn't make it the right equation.
 
  • #63
Well, I got to concede to the greater wisdom. I don't quite have my head around it, but I guess what I'm hearing is that there are multiple independent ways of envisioning lift, each of which explains it, fully, in a different way.
 
  • #64
A great many things can be looked at multiple ways, depending on your personal preferences, provided input data and needed output. Indeed, Newton's third law tells us that all forces come in pairs, and that's kind of what we are looking at with the two methods here. I would say that though you can often get the correct answer two different ways, being "complete" means understanding both.

I like the pressure profile around the wing because it speaks to me and is visual. But for a helicopter, it tends to make more sense to view the issue from the momentum of the rotor downwash.

If someone wants to start from scratch though with "how much lift will this airfoil shape I just designed create?" that's a very difficult question to answer, going far beyond a simple/superficial pressure summing/momentum change.
 

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